Flux distributing insulator



Oct. 6, 1936. E. c. VROOMAN' 2,056,813

FLUX DI STRIBUTING INSULATOR Filed March 3, 1933 amnion zawam a 19700 6 UNITED STATES Patented Oct. 6, 1936 PATENT OFFICE FLUX DISTRIBUTING IN SULATOR Edward C. Vrooman, Schenectady, N. Y., as- .signor to Locke Insulator Corporation, Baltimore, Md., a corporation of Maryland Application March 3, 1933, Serial No. 659,575

11 Claims.

The invention relates to insulators, particularly but not necessarily those used in association with currents at radio frequency, and has for its general object the provision of a novel insulator designed to equalize or distribute the electrostatic flux whereby the flux density may be controlled and undesirable heating effects eliminated.

It is known that a dielectric can be considered as a conductor of flux somewhat analogous to the manner in which iron conducts magnetism. By way of explanation it might be mentioned that if the magnetic flux in a bar of iron is maintained ata constant value by means of a direct current coil" it flows through certain definite, unchanging paths within the iron and along certain leakage paths outside the iron. This phenomenon is well understood by those interested and skilled in the art. If the bar of iron be magnetized by means'of an alternating current, the magnetic flux changes with each change of direction of the current flowing through the magnetizing coil. The magnetic fiux'follows certain paths within the iron bar and due to hysteresis and eddy ourbar, that is within the magnetizing coil, will travel only a short distance through the bar and will then leave the bar and prefer to travel through the air rather than'be crowded in with the other lines of flux that are within the bar.

In other words, if the density of magnetic flux is one hundred lines per square inch in that section of the bar within the coil, it may decrease to a much lower value, for example say thirty lines, at the ends of the bar located some distance from the coil. The bar could not maintain a uniform temperature throughout its length due to theactionof the different flux densities in the diiferent. portions. However, conduction and convection would play their part in equalizing the temperature. With this analogy in mind let us now consider a tube made of a dielectric material, for instance porcelain. Assuming that one end of this tube is raised to a high potential by means of radio frequency power and that the otherend of the tube remains at ground or a relatively low potential, if the tube be uniform in cross section, the flux density at the high voltage end would be very great and the greatest amount of heatwould be generated at the point offgreatest flux density. "At the grounded end would be relatively low and the heating effect would be much less than at the high voltage or potential end.

From a series of experiments as well as from mathematical calculation I have found that there is a very noticeable and in fact objectionable heating set up within the porcelain for the reason that porcelain is not a perfect insulator. This heating is a function of the frequency of electrical oscillations which, of course, is very high with radio power. It is a function of the number of flux lines or the iiux density per unit of area and is a function of the resistance to the flux flow. The heat generally will cause a rise in temperature above the surrounding air which is proportional to the amount of heat which will be dissipated per unit of area of the porcelain surface and to the rise in temperature above the normal. The above two relations can probably be expressed by the formula in which is the frequency, :1: is the flux density per unit, R is resistance per unit of area, K is the radiating constant, A is the surface dissipating heat, and t1 minus to is the temperature above normal. We are interested in two things: one is not to waste any more power than is necessary, which can be done by modifying the values on the left hand side of the above equation. If the area is increased at the point of maximum flux density the flux density will be decreased. In accordance with my invention I propose to do this by increasing the porcelain or other dielectric thickness at the high potential end of the insulator. This will of course reduce the temperature rise. I further contemplate reducing the temperature rise by working upon the right hand side of the equation, namely by increasing the area of radiation.

It is with the above facts in view that I have devised the present invention which, as mentioned above, has for its principal object the provision of an insulator of such formation that the flux density will be substantially uniform throughout so as to avoid excessive heating effects at the high potential end. I

A more specific object of the invention is to provide an insulator in which the dielectric is of variable thickness and area, the maximum of both characteristics being at the high potential end and the thickness as well as the area decreasing gradually towardthe low potential end so as to bring about the proper distribution of the flux density.

A still more specific object of the invention is to provide an insulator in which the increase in thickness and external area at the high potential end may be obtained by the simple expedient of providing the insulator with a series of longitudinally extending flutes which taper, the portion of greatest diameter being adjacent the high potential end and the flutes merging or fading into the intermediate portion toward the low potential end.

Mechanically considered, it is an object of the invention to provide an insulator having these characteristics and which will yet at the same time be easily capable of manufacture without any marked difficulty or any appreciable increase in the cost of production.

To the attainment of the foregoing and other objects and advantages, the invention preferably consists in the detailed construction to be hereinafter more fully described and claimed, and. illustrated in the accompanying drawing in which:

Figure I is a side elevation, with parts broken away and in section showing an insulator constructed in accordance with my invention,

Figure 2 is a cross section taken on the line 22 of Figure 1, and

Figure 3 is a cross section taken on the line 3-3 of Figure 1.

Referring more particularly to the drawing, it should be noted at the very outset that while I have illustrated an elongated tubular insulator this is simply for purposes of explanation as there is no intention whatsoever to limit the invention to an insulator of this particular variety as the principle involved may be applied to insulators of the post, pedestal and in fact other types.

In the present instance I have shown an elongated tubular body ID of cylindrical form and constructed necessarily of some appropriate dielectric material, preferably though not necessarily porcelain. The relative diameter of the central bore II with respect to the external diameter may be varied within considerable limits depending upon manufacturing conditions or necessities. At each end this body is represented as equipped with a cap l2 secured as by cement l3. The portions of the body within the confines of the caps may be left unglazed or may besanded or otherwise roughened to provide an adequate grip for the cement so that the caps will be secure. This is in accordance with well known practice. In the present instance the caps are represented as of the clevis type but this is immaterial as they might be of any other well known or preferred pattern.

In accordance with the invention the insulator body is of increased thickness as well as external area at the high potential end, which in the present case is adjacent the upper cap. Naturally this is of course dependent upon which end of the insulator is live that is to say connected with the power line. It is conceivable that the increase in thickness might be accomplished simply by tapering the bore H or by tapering the exterior, the portion of larger diameter being adjacent the upper cap. However, it is my intention not only to increase the thickness but to increase the external surface or radiating area. I have found that all the purposes of the invention can be brought about by fluting the exterior of the insulator, that is to say by forming it with a series of longitudinally extending ribs l4 spaced appropriate distances apart and tapering off from adjacent the upper cap, or the lower as the case might be, and fading or merging into the intermediate portion of the body at a point spaced from the other cap as clearly shown.

Considered from a manufacturing viewpoint, the body l0 may conveniently be extruded through a suitable die so as to have the ribs extending throughout the length. The extruded tube is of course cut into sections of the desired length and the sections while in a still more or less plastic condition may be turned in a lathe or its equivalent and the ribs or flutes cut away entirely for the necessary distance at one end and tapered throughout the remaining length. The final step of dressing may consist in rubbing the still green or plastic body lengthwise so as to smooth off and round the edges of the flutes or ribs as clearly indicated in Figures 2 and 3. After this preliminary treatment the body, if formed of porcelain, is dried, glazed and fired in the well known manner. The caps of whatever type is preferred are then applied and the insulator is ready for service.

Considering the device from an electrical viewpoint, I have found that the provision of the ta pered flutes or ribs and the resultant increase in thickness of the material at the high potential end is of great importance in that the increase in thickness will serve to effect a proper distribution of the flux flow through the dielectric material, this distribution operating to prevent objectionable heating effects in accordance with the discussion at the introductory part of this specification. Moreover the tapered flutes or ribs will provide a greatly increased exterior surface which will give a large area in contact with the air and operate to dissipate whatever heat is generated so that the temperature rise will be kept at the minimum notwithstanding the fact that the insulator may be used in connection with currents of high frequencies.

From the foregoing description and a study of the drawing it will be apparent that I have thus provided a very simply constructed insulator possessing the striking characteristics of controlling or distributing the flux flow and therefore preventing the generation of excessive heat, together with the feature of dissipating the very slight amount of heat which may be developed under the most adverse conditions. The insulator may be constructed cheaply as it requires no radical departure from the usual methods of manufacture and requires no unusual apparatus. It is thought from the above that the formation or construction and advantages in operation will be readily understood by one skilled in the art without further explanation.

While I have shown and described the invention as carried out in or applied to an insulator of the elongated tubular type, it should be distinctly understood that there is no limitation in this respect and that the right is reserved to make all such changes in the mode of application, manner of formation and in fact all variations as will constitute no departure from the spirit of the invention or the scope of the claims hereunto appended.

Having thus described the invention, I claim:

1. A flux distributing insulator comprising a dielectric body having metallic terminal fittings, said body being externally tapered whereby the portion of maximum diameter will be adjacent one fitting, the diameter gradually decreasing toward a point spaced from the other fitting, said tapered portion having longitudinal corrugations.

2. A flux distributing insulator comprising a dielectric body equipped at its ends with metallic fittings, said body being formed with longitudinally extending tapered flutes for gradually increasing the thickness toward one end and for providing increased radiating surface at said end.

3. A flux distributing insulator for use in connection with currents of radio frequencies, comprising a dielectric body equipped at its ends with metallic fittings, said body being formed with a series of longitudinally extending ribs having their maximum degree of projection adjacent one fitting and merging at their other ends into the body at a point spaced from the other fitting.

4. A dielectric body for interposition between metallic fittings, said body having one end portion formed with longitudinally extending ridges merging at one end into the intermediate portion of the body and increasing gradually in projection toward said end of the body.

5. A dielectric body for interposition between metallic fittings to form an insulator, said body being of elongated cylindrical form and of hollow construction with one end portion formed with a series of evenly spaced outwardly extending ribs springing from the intermediate portion of the body and flaring outwardly toward one end.

6. A dielectric body for interposition between metallic fittings to form an insulator, said body being of elongated cylindrical form and of hollow construction with one end portion formed with a series of evenly spaced outwardly extending ribs springing from the intermediate portion of the body and flaring outwardly toward one end but terminating short thereof to leave a smooth cylindrical terminal for receiving a fitting.

7. In a flux distributing insulator, a dielectric body having both end portions of substantially the same diameter, the body being formed with a circumferential series of outwardly extending ridges originating at the intermediate portion thereof and of gradually increasing extension to a point adjacent one end so as to produce increased area.

8. A flux distributing insulator comprising an elongated dielectric body formed intermediate its ends with a series of tapered ridges projecting outwardly therefrom and having their maximum degree of projection adjacent one end.

9. A flux distributing insulator comprising an elongated dielectric body adapted for disposition between metallic terminal fittings, said body having its end portions cylindrical and having its intermediate portion conical from a point spaced from one end to a point adjacent the other end, said conical portion being longitudinally fluted.

10. A flux distributing insulator comprising an elongated dielectric body having a cylindrical bore of uniform diameter therethrough, the intermediate portion of said body being conical from a point spaced from one end to a point adjacent the other end, the maximum diameter being at said other end, said conical portion being fluted to define alternating ridges and grooves.

11. In a flux dstributing insulator, an elongated cylindrical dielectric body having a cylindrical bore of uniform diameter, said body being formed with a circumferential series of tapered ridges originating at a point spaced from one end and continuing to a point adjacent the other end whereby the greatest thickness of material and area will be adjacent said other end.

EDWARD C. VROOMAN. 

